The use of lanthanide ions to probe protein structure via fluorescence and nmr spectroscopy has been shown to be a useful and interesting tools by many investigators. The application of these techniques to the muscle system has been sparse. This proposal incorporates plans to utilize the fluorescence properties of the terbium (Tb3 ion) and the europium (Eu3 ion) to investigate the structure, and binding properties of the calcium binding component in rabbit skeletal muscle, troponin-C and its interaction with other components of the contractile system. This protein contains four (4) calcium binding sites. Using a cyanogen bromide cleavage and a trypsin digest, peptides which bind a single calcium ion and two calcium ions respectively will be isolated. The fluorescence behavior of lanthnides bound to these fragments of TNC will be compared to the behavior of the whole protein, in order to isolate the individual calcium binding sites. Once this has been established, the lanthanide ions will be used to investigate the interactions that occur when the isolated components of the muscle system, suitably modified are recombined.